In a common form of modern rock-drilling apparatus, the drill motor is mounted for extension and retraction hydraulically along a strut the foot of which may be forced against the surface to be drilled. Such a strut is mounted on a tractor built for the purpose of moving the strut from place to place. Such drilling apparatus is used on building sites, road work, in mines and tunnels and can be moved reasonably quickly from point to point. The use of such a machine to drill holes in rock lined ditches is limited in depth of water because of the following: a. the arm is too short to operate from outside the ditch, b. moving the tractor in the ditch is limited by the depth at which the operator can wade alongside the machine, and c. the condition of the surface at the bottom of the ditch which the machine must traverse. When holes are drilled under water with such apparatus, nothing prevents the debris which has collected at the bottom of the ditch and the drill debris from falling back into the hole, and when the hole has been cleaned, filling of the hole with explosives is awkward because it is under water.
Means to limit the flow of debris into a hole drilled in submerged rock as found in the prior art include a short mud guard tube as in Hansen U.S. Pat. No. 1,645,989 which is lowered to the bottom by the submerged weight of the mud guard plus the drill motor, and a long telescopic sand guard in Hansen U.S. Pat. No. 1,697,649 lowered to the bottom by the submerged weight of the lower section of the sand guard.
The method of loading explosives into the hole drilled in submerged rock described in the prior art is to place the charge through the telescopic sand guard tube of Hansen U.S. Pat. No. 1,697,649 after raising the drill motor and removing the drill steels from the drill motor and sand guard. Bourne in U.S. Pat. No. 371,298 shows the use of a filling tube for placing explosives in a dry land hole so that in successive steps an enlarged cavity may be formed at the bottom of the hole to receive a large explosive charge, however, the use of such a filling tube as taught by this patent would require the services of a diver.
The method in which the drill may be moved from one hole location to another as taught in the prior art is limited to the use of a special boom mounted on anchored barges as in Hansen U.S. Pat. Nos. 1,697,649 and 1,778,320.
The placing of explosives in holes in submerged rock as accomplished prior to my invention is thus a long process because of the time taken to locate the hole, drill the hole (possibly changing drills in the process as in Hansen U.S. Pat. No. 1,645,989), keep the hole clean, charge the hole, and move the drill to the next location.